In recent years, in order to achieve further improvement of the performance of semiconductor devices, a method in which a semiconductor element is made into a face down structure and mounted on the wiring circuit substrate such as a wiring circuit-formed mother board, daughter board or the like (flip chip system, direct chip attach system or the like) is drawing attention. That is, the conventional mounting methods have various problems in terms of their performance, such as a delay of information transfer by the wiring and generation of information transfer error due to cross talk, which occur sometimes when a semiconductor element is mounted on a wiring circuit substrate in a packaged form by making contact from it on the lead frame with a gold wire.
In contrast, in the mounting method of face down system, the surface electrode of a semiconductor element is directly connected to a wiring circuit substrate so that it can provide a thin and light semiconductor device. However, in the method such as a flip chip system, direct chip attach system or the like, a semiconductor element and a wiring circuit substrate each having each own different coefficient of linear expansion are directly connected electrically, so that improvement of reliability of the connected part is an important issue.
For the purpose of resolving such issue, a method has been employed in which reliability of the connection is improved by injecting a liquid thermosetting resin which is called an underfill material into the gap between a semiconductor element and wiring circuit substrate, forming a hardened resin body by hardening this, and thereby distributing the stress concentrated into the electric connection part into said hardened resin body.
However, in order to effect injection of a liquid thermosetting resin into the gap between a semiconductor element and wiring circuit substrate, it is necessary to secure a space for arranging an injection nozzle in the peripheral of the semiconductor element mounting position. Since it becomes difficult to secure such a space as miniaturization and thinning of semiconductor devices progresses, demand has been directed toward the improvement of the liquid resin inflow (underfill) step.
Because of this, a method for producing a semiconductor device using an underfill in a film structure has also been devised. According to such a method which uses a film for underfill, it is necessary to seal the gap between the substrate and chip by melting and hardening the film at the same time with the connection of electrodes. Since this requires bonding conditions of high temperature, high load and long time, there is a possibility of causing damage to the pad and substrate and exerting a bad influence by the residual stress upon the reliability. Thus, there is a demand for an adhesive film for underfill use, which can be used under bonding conditions of lower temperature, lighter load and shorter time.